1. Field of the Invention
The present invention relates to a roller type transmission device in which some of pin rollers always mesh with the respective teeth of a ring gear, and particularly concerns a roller type transmission device which is improved to achieve a high reduction ratio with a high precision.
2. Description of Related Art
As a general differential speed reducer device, a roller-type speed reducer device has been introduced by Japanese Laid-open Patent Application Nos. 2006-300338, 2006-329431 and 01-169154 (referred simply to as references hereinafter).
The speed reducer device of these references has been employed to a canti-lever arm of an industrialized robot in order to reduce the speed from an electric motor powered with a high revolution but a low torque.
The speed reducer device has an outer gear ring and an inner gear ring, a central portion of which has an eccentric shaft as an output ring. The outer gear ring has an outer side which has a multitude of wavy teeth circumferentially profiled in a cycloidal fashion. The inner gear ring is placed to surround the outer gear ring, and has an inner side surface which has a multitude of columnar pins circumferentially placed at regular intervals. The outer gear ring corresponds its outer teeth to the pins of the inner gear ring, and determines the number of the outer teeth to be less than the number of the pins by the difference of one.
Upon operating the speed reducer device, the outer teeth rides over the pins to rotationally move the inner gear ring by a pitch distance of the pins. Since the outer teeth rides over one pin when the eccentric shaft rotates by one single turn, the speed reduction ratio is expressed by an inverse number of the outer teeth. When the number of the outer teeth is counted as 40, the speed reduction ratio is calculated as 1/40.
In each of the above references, the inner gear ring has the inner side surface which forms a multitude of grooves (U-shaped in cross section) circumferentially arranged in parallel at regular intervals. Because the pins are presumably press fit into the respective grooves to embed the pins into the inner side surface of the inner gear ring,
it becomes necessary to precisely arrange each of the grooves at equal distance, width and depth while keeping an appropriate straightness of the grooves, thereby requiring microadjustment processes including such as, for example, a grinding procedure. The neighboring grooves are required to keep a little distance therebetween, which makes it difficult to reduce the inner gear ring in a diametrical dimension so as to defy to render the whole structure compact.
In order to take out only the rotational movement from the compound movement consisting of the rotational movement and the revolving movement, an adjustment mechanism is provided which forms an adjustment plate defined on the inner gear ring to have a plurality of openings arranged along a certain pitch circle on the adjustment plate. The adjustment plate has pins provided on the outer gear ring in registration with the openings. However, the mechanical principles has been studied to develop a simple adjustment mechanism without using the conventional adjustment plate and pins. This is because the conventional adjustment mechanism increases the number of the working processes upon assembling the adjustment mechanism, thus making it difficult to reduce the size of the adjustment plate so as to defy to render the whole structure compact.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide a roller type transmission device which is capable of minimizing a backlash phenomenon, rendering a pitch distance precise between the pin rollers, maintaining a uniform tooth profile with a high precision, equalizing a surface roughness and improving a meshing precision between meshing portions, and reducing the number of assembly processes to reduce the manufacturing cost conducive to mass production.